In order to maintain the quality of service in communication networks, it is necessary to limit the number of calls allowed onto the network. The optimum number of calls to be allowed on the network is determined by the characteristics of the network which depend on trunk speeds and other hardware constraints, such as buffer sizes. The mix of call types and the relative number of each is also an important consideration.
Where a user of a network knows the mean bit rate of the call he wishes to place on the network, it is possible to use methods which employ Convolution or Large Deviation Approximation techniques to determine whether the call can be carried by the network without the quality of service dropping below a minimum value. However, in practice the user is unlikely to know what the call's mean bit rate will be. This will be especially the case where the network carries broadband services. It has been proposed to monitor the network's traffic load and to refine the control method in a dynamic way. This type of method has been called dynamic Connection Admission Control (CAC).
Given the uncertainties surrounding the data type that will be carried on communication networks offering broadband services, there is a generally held belief in the communications field that it will not be possible to employ statistical multiplexing techniques on networks that employ asynchronous transfer mode techniques (ATM).